1. Field of the Invention
This invention relates to packing film.
More particularly, the present invention relates to composite films for packing comprising a plurality of film-forming polymer layers, having a high separation resistance between one layer and another and having a low permeability to gases and vapor.
By virtue of these particular properties, the films according to the present invention are particularly suitable for the manufacture of containers, envelopes, bags, vessels and manufactured articles in general, which are chiefly intended for the packing industry.
2. Description of the Prior Art
As is known, materials to be used for packing desirably possess a combination of mechanical and aesthetic characteristics, including non-permeability, thermoweldability and other characteristics, which are rarely simultaneously found in films prepared from only one type of polymer.
For this reason, bonded articles or laminated articles obtained from a combination of more than one film of different materials, or lacquered films are generally utilized.
Thus, for example, there are known bonded articles and laminated articles manufactured from polyolefinic films with films of other thermoplastic polymers and/or with metal sheets, such as aluminum sheets.
There are also known bonded articles prepared from polypropylene oriented films with non-oriented films obtained from mixtures of polypropylene with polyethylene or of crystalline ethylene-propylene copolymers.
The lacquered films are obtained by applying onto a base or supporting film one or more layers of different polymers.
The main drawback encountered in preparing these bonded, laminated or lacquered films is the inconsistency or low adhesion of the different polymers or copolymers which the various layers are made from.
As is known, in order to overcome this drawback, use is made of adhesives interposed between the various layers, and of surface treatments, such as electric discharges, chemical oxidation, and flame treatments, carried out prior to bonding or to lacquering.